Composite materials have been produced by a variety of different processes and techniques. Composite materials have been formed by casting one metal within another metal, cladding one metal to another, deforming or pressing two different metals together and variations of these methods. A problem with composite materials is the tendency for composites to have anisotropic properties. Inadequate bonding between the two materials of a composite can cause composites to be anisotropic and to perform at less than theoretical levels. Unclean surfaces, such as surfaces that contain metal oxides, interfere with bonding between two materials. Generally, bonds containing metal oxides have less than ideal properties.
Recently, in an attempt to produce a composite having a low coefficient of thermal expansion and a high thermal and electrical conductivity, a thin metallic composite structure was developed. The composite structure was formed by first piercing several holes through an inner layer of low coefficient of thermal expansion metal, placing two opposing layers of metal having high thermal and electrical conductivity on opposing sides of the inner layer to sandwich the inner layer and hot rolling the sandwiched inner layer. During the hot rolling, the outer layers plastically deform to fill the pierced holes of the inner layer. The inner layer may be electroplated after the piercing holes are made, to improve the bonding between the inner and outer layers during the hot rolling step. Although initial tests for the above method have performed satisfactory, it is believed that the method of the invention may in fact provide improved performance.
An object of the invention is to provide a method of producing thin metallic composite structures with improved bonding between metals of varied composition.
It is another object of the invention to provide a method of producing thin metallic composites having an inner layer completely filled with the metal of the outer layer.
It is another object of the invention to produce a metal composite having the demanding properties of low thermal expansion in combination with high thermal and electrical conductivity.